In many situations and locations, normal electrical power is unavailable due to a failure of the electrical grid or remoteness of location. Charging rechargeable battery devices or directly powering electrical appliances are significant challenges when normal electrical power, such as AC service, is unavailable. Battery power provides a means of operating away from electrical mains, giving rise to a large number of different battery powered devices. However, common battery formats tend to be optimized for service intervals convenient when grid power is available for recharging or when grid powered infrastructure, such as retail outlets, are available for distribution of new batteries.
In situations where grid powered services are unavailable, then either a large store of replacement batteries must be cached, or some other form of battery recharging is required. Caching of supplementary batteries poses a problem due to both the low energy density of conventional batteries and also because of self-discharge issues, which can limit the life expectancy of the battery cache.
Supplementary non-grid charging systems exist and may be used. Examples include solar powered chargers, hand crank chargers, other forms of kinetic chargers or energy scavenging devices. These all share various deficiencies, such as requiring large formats, dependency on local environmental conditions to generate power and insufficient power generation to operate most devices.